1. Field of the Invention
The present invention relates to a microlens array, to a manufacturing method for this microlens array, and to a display device using the same microlens array.
2. Description of the Related Art
Microlens arrays comprising a large number of very small lenses arranged in an ordered array have been used in liquid crystal display (LCD) panels and other applications. Using a microlens array in an LCD panel makes it possible for each lens to focus incident light on an individual pixel, and thereby achieve a bright display.
Microlens arrays can be manufactured using both dry etching and wet etching methods. A drawback to both dry and wet etching methods is the need for a lithography step in the production of each microlens array, thus increasing manufacturing cost.
To resolve this problem, Japan Unexamined Patent Application Publication (kokai) 3-198003 teaches a method for manufacturing a microlens array without using a lithography step. This method uses a master having formed thereon curved surfaces corresponding to each of the lenses in the microlens array. A resin is then deposited on this master, set, and removed from the master.
This method in effect uses the master as a mold to form the microlens array in a transfer molding process, and thus eliminates the lithography process required by conventional wet and dry etching methods for each microlens array. Once the master is prepared it can be reused repeatedly insofar as the durability of the master permits. The per-product cost of the master therefore decreases as the durability of the master increases, and this contributes to lower product (microlens array) cost.
A drawback to this method is that the master is used in the production of each product, leading to contamination and wear of the master, and therefore faster deterioration of the master. This deterioration is apparent as deformation of the pattern shape. Lithography is also used to manufacture the master. The cost of master manufacture is therefore high, and an increase in the frequency of master manufacture is thus a factor in higher unit cost for each product.
To resolve the aforementioned problems, an object of the present invention is to provide a method for manufacturing a microlens array at low cost by reducing the frequency with which high cost microlens array masters must be manufactured.
A further object of the present invention is to provide a microlens array manufactured with the manufacturing method of the invention.
A first microlens array manufacturing method according to the present invention comprises: a first step for forming a master having a plurality of first curved surfaces; a second step for forming a duplicate master having a plurality of second curved surfaces transferred from the first curved surfaces; and a third step for forming a light transmitting layer having a plurality of lenses transferred from the second curved surfaces.
A manufacturing method according to the present invention thus produces a duplicate master of a master having a plurality of curved surfaces, and uses this duplicate master to produce the individual microlens arrays having a plurality of lenses.
With this method a high cost master is therefore used only when producing a duplicate master, thus reducing deterioration of the master and the frequency with which the master must be manufactured again. Microlens array production cost is therefore reduced.
The duplicate master produced with this first microlens array manufacturing method according to the present invention can be manufactured by forming a metal layer using an electroforming process on the first curved surfaces side of the master, and then separating this metal layer from the master. A duplicate master can be easily produced by thus using an electroforming, particularly an electroplating, process.
A second microlens array manufacturing method according to the present invention comprises a first step for forming a master having a plurality of first curved surfaces; a second step for forming an intermediate master having a plurality of second curved surfaces transferred from the first curved surfaces; a third step for forming a duplicate master having a plurality of third curved surfaces transferred from the second curved surfaces; and a fourth step for forming a light transmitting layer having a plurality of lenses transferred from the third curved surfaces.
This second manufacturing method of the present invention produces a duplicate master using an intermediate master manufactured from the original master. There is thus greater freedom in the methods that can be used to manufacture the duplicate master, and in the materials that can be used for the master and the duplicate master. The shape of the curved surfaces can also be transferred with high precision, and the durability of the master and duplicate master can be further improved.
In this second manufacturing method according to the present invention, the second step for forming an intermediate master preferably comprises: a step for coating an intermediate master precursor on the first curved surfaces side of the master; a step for setting the intermediate master precursor to form an intermediate master; and a step for separating the intermediate master from the master. The intermediate master precursor in this method preferably contains a material that can be set by applying energy, for example light or heat, to the precursor material. A thermoplastic precursor can also be used.
Further preferably, the intermediate master is made from a resin material.
In this microlens array manufacturing method the duplicate master is preferably obtained by forming a metal layer by an electroforming process on the second curved surfaces side of the intermediate master, and then separating this metal layer from the intermediate master.
In both of the above first and second manufacturing methods, the step for forming a light transmitting layer preferably comprises: a step for coating a light transmitting layer precursor on the curved surfaces side of the duplicate master; a step for setting the light transmitting layer precursor to form a light transmitting layer; and a step for separating the light transmitting layer from the duplicate master.
The light transmitting layer precursor further preferably contains a material that can be set by applying energy, preferably light or heat, thereto. The light transmitting layer precursor can also be a thermoplastic material. The light transmitting layer is also preferably made from a resin material.
The first curved surfaces of the master are preferably formed by lithographic and etching processes because of the high precision of these processes. Etching methods are particularly desirable when forming the first curved surfaces because the first curved surfaces are the basis of the final lenses.
The master is further preferably made of silicon or quartz. Silicon and quartz provide excellent surface smoothness, and can be easily processed using lithographic and etching methods.
High performance microlens arrays can therefore be manufactured using the first or second manufacturing method of the present invention.
The present invention further provides a display device comprising a microlens array manufactured using a method according to the present invention, and a light source for emitting light towards the microlens array.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.